Mozilla overhauls its brower's Windows look and adds a range of new features, including support for HTML5 and the WebM video standard

Mozilla on Tuesday released the first beta of Firefox 4, a major upgrade expected later this year that features a revamped interface, support for a wide range of Web technologies, and performance increases.

Firefox 4 Beta 1, which missed its original end-of-June ship date by less than a week, is available for Windows, Mac, and Linux , although the most obvious changes -- the reworked interface -- is only offered automatically to Windows users.

"We moved the tabs to the top to make it easier to focus on the Web content and easier to control the tools in your Web browser," said Mike Beltzner, director of Firefox, in an introductory message on the Mozilla blog. "Also, if you have Windows 7 or Windows Vista, the menu bar was replaced with a single Firefox button so you can get to the most-used options with just one click."

The tabs-on-top look is present by default only in the Windows version of Firefox 4. Mac and Linux users can switch on the UI feature from the View menu by selecting Toolbars and then Tabs on Top.

Mozilla has been talking about and working on a visual refresh for Firefox since November 2009, when it said it would borrow elements from both Microsoft's Windows 7 and Google's Chrome browser.

The similarities between Firefox 4 and Chrome are hard to miss: Both put the tabs above the address bar; both sport a minimalist look with few buttons; and on Vista and Windows 7, both dispense with the traditional menus spread across the top of the screen.

Firefox has gone one better than Chrome on that last element, for a single button -- marked "Firefox" -- displays a drop-down menu when clicked. Chrome uses two buttons for the same result.

All editions of Firefox 4 include a new crash protection feature, called "out of process plug-in" or OOPP for short. OOPP, designed to protect the browser from crashes by Adobe's Flash, Apple's QuickTime or Microsoft's Silverlight, debuted in the Windows version of Firefox 3.6.4, but until Firefox 4 Beta 1, wasn't available to Mac or Linux users.

Also under the hood are multiple performance improvements and standards support additions. The browser boasts a new HTML5 parser; native support for the WebM video standard that Google introduced two months ago; and unspecified performance gains that Beltzner said were just the beginning for Firefox 4.

Some of the features expected to make the final version are already tucked into the browser but have been turned off by default. Among them are support for WebGL and hardware acceleration based on Windows Vista's and Windows 7's Direct2D, the same API (application programming interface) Microsoft uses to speed up Internet Explorer 9.

Mozilla has set an aggressive schedule for Firefox 4. In May, Beltzner said the company was shooting for a final by the end of November, with a solid release candidate in mid-October. Tuesday, he told users to expect beta updates every two to three weeks.

Firefox accounts for approximately 23.8 percent of all browsers in use, according to the most recent data from Web metrics company Net Applications. The browser peaked last November at 24.7 percent. In the same seven months, Google's Chrome nearly doubling its usage share, going from 3.9 percent to 7.2 percent.